This invention relates to a process for the preparation of olefins, particularly aryl diolefins. The process is particularly useful for the preparation of diolefinic polymerization initiators such as m-bis-(1-phenylethenyl)benzene.
A variety of methods are known for preparing unsaturated compounds having one or more carbon-carbon double bonds. Both aliphatic and aromatic olefins and diolefins are prepared commercially by pyrolysis of saturated hydrocarbons. Other methods include reacting an unsaturated alcohol and a ketone or an aldehyde in the presence of carbon monoxide and a catalyst comprising a hydrohalo salt of a Group VIII metal and a germanium or tin salt, and disproportionation and dehydrogenation of more saturated compounds.
Another preparation involves reacting isophthaloyl chloride with benzene. One problem with this approach involves the hazards of handling benzene.
Some of the best methods for preparing aliphatic and aromatic olefins and diolefins involve the dehydration of alcohols. An aromatic diolefin can be prepared by reducing an acylated alkyl halide-substituted aromatic compound to the corresponding aromatic alcohol, dehydrating the alcohol to obtain a vinyl substituted aryl alkyl halide and thereafter subjecting the alkyl halide moiety to dehydrohalogenation conditions to recover the diolefinically-unsaturated aromatic compound. In another process, alcohols are dehydrated and oxydehydrogenated by passing an alcohol-halogen-oxygen mixture over a substantially inert contact-surface such as Alundum and then passing the mixture over a metallic oxide catalyst such as copper chromite to produce dienes such as isoprene.
Among the methods best adapted to the synthesis of aliphatic and aromatic olefins and diolefins in quantity are those which involve the use of the Grignard reaction. In these reactions, an aldehyde, ketone or ester is reacted with a Grignard reagent to form a carbinol. The carbinol is dehydrated to produce an olefin or a mixture of olefins which usually can be separated by fractionation. Typically, in forming olefins and diolefins from alcohol precursors via the Grignard reaction, the alcohols must be separated from their reaction mixture and dehydrated in the presence of acidic catalysts such as paratoluene sulfonic acid, silica gels or aluminum oxides in order to obtain reasonable yields and to inhibit the formation of undesirable by-products. Even when the alcohol is separated from its reaction mixture, the dehydration step will result in formation of undesirable by-products and unacceptable yields unless the dehydration reaction conditions are carefully controlled.